Some kids just HATE high-chairs. Both my kids HATED it. It is like being jailed... it is like a punishment. High chairs are a pain.
No, you do NOT have to have a child in that to feed them. If it does not work and the child hates the high-chair, why use it?
There are kids around the world, who do not have high-chairs, and they eat fine... at a kid height table... or just on a regular chair, or a booster chair... or at the coffee table, or by sitting on the floor at a table, etc. Its fine. In some cultures, they do eat at a low table sitting on the floor.
My kids, if at our dining table/kitchen table... just like to sit on the regular chair themselves... kneeling on it. They hated any contrivance of a high-chair.
The thing is: you do not want to make eating... a hated thing. It should be something nice and fun and pleasant for the child. Not a battle. If it is a battle, then it always will be. Just to eat. Not good.
Sure, when he is older and taller... he CAN eat at the table, like an "adult." There is LOTS of time, to do that... and for him to learn that. As you said... just make sure he eats.... and to me, a child does not HAVE TO be put in a high-chair. Just feed him in a place and in a way... that is productive... and NOT a battle.
I fed my kids... on the coffee table or on a kiddie table with kid sized chairs. They LOVED that.
Perhaps... get your son a kiddie sized table and chair... and he can use it to eat... and to do other things on. It is very useful. I highly recommend that.
All the best,
Susan